After getting in touch with Nabble, I was asked to resubscribe our lists.
Sven did this for me, and I am pleased to report that a test post sent to
each Forum has turned up in the list and in the Nabble Forum. However, there
was a difference - a delay occurred before Nabble showed the post. Also - it
seems I was not offered the option to have email notifications of replies.
Hopefully our problems are now over.